The present invention relates to device making it possible to demodulate frequency-modulated waves and in particular simple devices operating up to carrier frequencies of a few dozen megahertz.
In order to demodulate a frequency-modulated wave, it is known to generate from said wave pulses of a given length and which are independent of the modulated wave frequency. These pulses are then integrated in order to obtain a mean value for these pulses which is proportional to the repetition frequency thereof and therefore to the frequency of the modulated wave.
There are numerous devices making it possible to perform this function and the most efficient of these uses a clipping circuit arranged in series with a monostable multivibrator and a low-pass filter.
The clipping circuit clips the frequency-modulated signal thus supplying square wave frequency-modulated signals from which the monostable multivibrator supplies pulses of predetermined, constant duration, and the low-pass filter extracts the mean value.
The disadvantages of this device are due to the necessity of having very short rise and fall times for these pulses if it is desired to obtain a correct operation (mean value of the signal obtained at the output from the device which is proportional to the frequency) at frequencies of a few dozen megahertz.